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What roles do airplane doors play in the flight process

What roles do airplane doors play in the flight process? By Ahmed Haouaria

05 Juil 2020
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Among the questions that intrigue many people who usually fly on an airplane, there is that of emergency exits.

In fact, when we talk about emergency exits, we are talking at the same time about main doors but also emergency exits, often located close to the wings, even if in aviation terminology we prefer the term '' exit '' for both: aircraft main door and Overwing exits.

How do aircraft exits work?

What essential roles do aircraft exits play in a passenger aircraft?

This is what we will see in this new post of aviation stars.

We will deal with the following key points:

1. Operation under normal conditions

2. Operation of doors in emergency conditions

3. Unserviceable exits

4. Actions to be undertaken by the Cabin Crew

5. Limitations on the number of unusable exits

6. Emergency evacuation device

 

1. Operation under normal conditions

Aircraft doors are used in normal operating conditions for passengers boarding and disembarking , they also serve for:

  • catering products loading
  • communication between the ground staff and the aircraft crew
  • aircraft cleaning process
  • engineering/maintenance team intervention

The sizes and distribution of the doors are the result of the facilitation of all these operations for the practical use of the crew, pilots and cabin crew, passengers and the various services involved in carrying out a flight operation before and after the flight. 

2. Operation of doors in emergency conditions

But more important than the functions mentioned above in normal conditions, the size, the number and the distribution of exits along the fuselage are the result of the application of strict safety rules: indeed, the certification of an aircraft requires that the cabin configuration allows evacuation of passengers and crew members in 90 seconds.

The aircraft manufacturer proceeds, for the purposes of certification, to an exercise / simulation of occupant evacuation using only half of the available exits.

An aircraft manufacturer must therefore, in order to meet this requirement, size and distribute the exits along its fuselage and symmetrically to the right and to the left, considering the case where the density of seats is maximum.

The devices for opening the exits must be simple to operate and their operation must not require excessive effort under the most unfavorable opening conditions.

The corresponding instructions for opening must be visible, easy to recognize and written in the airline country language, and at least another ICAO official language. The use of pictograms can also be used.

Each emergency exit must be fitted with a locking and protection device preventing it from opening in flight either following an untimely maneuver by the occupants, or following a mechanical failure of the normal opening system.

All passenger emergency exits, their means of access and their means of opening are clearly visible and comply with the following requirements:

  • The  location of the passenger emergency exit should be recognized at a distance equal to the width of the cabin;
  • The location of the passenger emergency exit is indicated by a sign visible to occupants approaching along each main passenger aisle;
  • On all aircraft with more than 30 passengers, a sign indicating the passenger emergency exit, near each exit;
  • The arrangement of the seats, their armrests and all other arrangements must allow easy access to the exits;
  • Cabin Evacuation/Emergency marker  must be able to be recognized as such at all times;
  • They must be clearly visible, for example using photoluminescent signs;
  • These signals must not be hidden by cabin  dividing curtains, decorations, etc.).

Certification requirements for civil [commercial] aircraft are derived from ICAO Annex 8 Airworthiness of Aircraft [ICAO, 2016] and the ICAO Airworthiness Manual, Part V State of Design and State of Manufacture [ICAO, 2014]. Each ICAO contracting state then establishes its own legal framework to implement the internationally agreed standards and recommended practices.

3. Unserviceable exits

You have understood that the most important role of an aircraft exit is that of ensuring the evacuation of passengers when necessary in the best possible conditions.

Therefore, certain considerations are taken into account when an exit is unserviceable.

Let's start first by defining an unserviceable exit.

An exit is considered unserviceable if one of the following exit components is inoperative:

  1. interior or exterior opening mechanism,
  2. opening assistance device,
  3. door open locking system; door in the open position,
  4. auxiliary means of evacuation/ Evacuation slides,
  5. aircraft cabin emergency lighting

Below is a description of the 5 components:

Interior or exterior opening mechanism

The interior or exterior opening mechanism is the tool that allows the cabin crew member to open the doors from the inside or, if necessary, from the outside. This system differs from one type of aircraft to another.

Let’s take the example of an Airbus 320:

This type of aircraft has four doors quipped with evacuation slides. 

From the inside, the flight attendants open the door by lifting the RED door handle upwards to the "Open" position to open the door.

From the outside, the flight attendant introduces his/her hand below the 'PUSH HERE' handle and lifts the handle upwards in the direction of the arrow.

If the door has been forgotten armed, that is to say, connected to the evacuation slide it will be systematically disarmed.

We will come back to this procedure later in a dedicated post.

For the case of the Boeing 737:

The Cabin Crew opens the door by moving the operating handle from the locked position to the open position under both conditions (normal and emergency).

For the opening from the outside, the Cabin Crew pulls the handle and proceeds to a left rotation which will trigger the opening of the door.

Please note that the Boeing 737 does not have the same systematic security for disarming the slide similar to the Airbus 320 , which requires ensuring that the door is properly disarmed before opening it from the outside.

Opening assistance device

Each door has an opening assistance device that allows the flight attendant to use it as a support to help open and close the door.

Door open locking system

To ensure that the door is locked in the open position, the Cabin Crew Member must push the door outwards and guide it with the operating handle to the ‘’ Locked open position''. 

The door locks automatically.

Auxiliary evacuation means

Each door has a single-lane or dual-lane slide with automatic inflation.

For the correct functioning of the A320 slide, for example, the door has:

  • a mechanical locking indicator for visual verification of the locking position "Lock" (green) and unlocking "Unlock" (red);
  • an Armed warning light (white);
  • a cabin pressure warning light (red);
  • a lever for arming and disarming the slides;
  • a single lane slides at each main door;
  • a dual lane slides at each emergency exit above the overwing exits.

In the case of the A320, the arming of the slide is done by controlling on the Arming lever by putting it in the “Armed” position and disarming by lifting the lever upwards to the “Disarmed” position.

For the B737, arm and disarm manually by inserting or removing a retaining bar on the floor fixing fittings.

For both types, the slide is deployed and inflated as soon as the Cabin Crew opens a door in the Armed position.

Emergency lighting

Emergency lighting is often a LED lighting, ensuring the recognition and use of evacuation slide and allowing the evacuation of the aircraft.

4. Actions to be undertaken by the Cabin Crew

Now that we have seen the essential components of the door with, if applicable, the designation of a door as unusable in the event of malfunction of at least one of these components, we will now see the actions to be taken by the Cabin Crew if a door is considered inoperative.

When an exit is unserviceable, the Cabin Crew Member must ensure the following:

  • ensure the appropriate functioning of the remaining exits;
  • close and lock the ensure the unserviceable exit,
  • hide the identification of unserviceable exit,
  • deactivate the elements of the emergency lighting leading to this exit,
  • place a very apparent inscription "INOPERATIVE" on the  concerned unserviceable exit.

5. Limitations on the number of unserviceable exits

An Airline cannot use an airplane for passengers transport purposes if:

  • more than half of the exits on the same side are unserviceable,
  • a pair of exits, (2 exits of the same type located on each side of the fuselage is unserviceable,
  • more than half of the exits on the same side cannot be used.

6. Emergency evacuation device

All aircraft must be equipped with devices to facilitate the evacuation of all passengers in the event of an emergency:

  • for single-level exits: if the distance between the exit threshold and the ground is greater than or equal to 1.83 m (plane on the ground with the landing gears extended),
  • for wing exits: when the trailing edge of the flaps extended is more than 1.83m from the ground.

 

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